Pregnancy calculator by weeks
Arrive with a week number (“I’m 16 weeks”) and get the rest of the timeline — trimester and approximate EDD — as of the day that week count was true. Estimate only — not medical advice.
Enter a date to see an estimate.
What this page does
Week-number-in is a first-class mode here. You must say which calendar day that week count referred to; otherwise the EDD back-calc is ambiguous.
We do not ship fruit charts. You get dating context: estimated due date from remaining days in a 280-day framework, plus trimester bucket.
When to use
You were told a week count at a visit and lost the paperwork; you want trimester from a week number.
When not to
Entering a week number without an as-of date is meaningless — the form requires both.
Assumptions
Browser-only planning arithmetic. Defaults are disclosed on the page. Ultrasound and clinic policy override this tool.
Examples
16 weeks 0 days · as-of Jul 17, 2026 → EDD ≈ Jan 1, 2027 (illustrative).
20 weeks 3 days · as-of Jul 17, 2026 → EDD + second-trimester hint.
Gotchas
Clinic dating after ultrasound can differ from browser math — the clinic wins for medical decisions.
Wrong input dates (retrieval vs transfer, spotting vs true LMP) slide every result.
Estimate only — not medical advice.
How this is calculated
The math stays in your browser. Enter the dates you actually know, read the estimate, and treat clinic ultrasound dating as the authority when it disagrees.
Nothing here is medical advice, a diagnosis, or a substitute for prenatal care.
- Enter the date(s) or numbers this page asks for.
- Check the assumptions under the result and on Methodology.
- Compare with your clinic portal if you have one.
- Use related tools if you only have a different kind of date.
- Confirm medical decisions with your clinician.
EDD ≈ asOf + (280 − (weeks×7 + days)).
Related calculators
How many weeks from LMP/EDD: how-many-weeks tool. Trimester buckets: trimester calculator. Multi-mode EDD: EDD calculator.
See also: trimester calculator, edd calculator, and pregnancy week calculator.
FAQ
- Can I start from weeks instead of LMP?
- Yes — enter weeks + days and the as-of date.
- Does this change my clinic EDD?
- No — planning only.
- What if I don’t remember the as-of day?
- Guessing invents error; use LMP/EDD tools instead.
- Fruit size charts?
- Not here.
- Trimester from weeks?
- Shown when GA maps cleanly.
- Is this medical advice?
- Estimate only — not medical advice. Confirm dating, testing, and medical decisions with your clinic.